First Alien 3 plans

a) Scenarios Leading Nowhere
The producers had
ideas ranging from the aliens invading Earth, where they fuse into a
giant, multi-talented monster that destroys New York City, which seemed
to be the basic scenario used for an Eric Red script although it takes
place on an offworld colony, to Ripley and Newt hunting an especially
mobile creature in a Blade Runner-eseque off-world Metropolis, and then
unsatisfied with these concepts, Hill, Giler and Carroll eventually
returned to what worked in the first two films, a dark, isolated,
labyrinthine setting.

b)Weyland Vs Seperatists scenario evolves
And they soon found themselves returning for
input, both because they had respect for her judgment and because they
thought she'd be more likely to reprise her role if they brought her in
as co-producer to help the story and Lieutenant Ripley evolve David Giler
and Walter Hill each labored on several ideas before settling upon a
complex two part story that offered the underhanded Weyland-Yutani
Corporation (known as "The Company") facing off with militarily
aggressive culture of humans whose rigid socialist ideology had caused
them to separate from Earth society. Weaver would only make a cameo
appearance in it and demanded that Alien 3 and 4 be produced
concurrently to lessen production costs.

c) Grabbing Ridley Scott's interest
The idea at
the time was that his version was intended to be directed by Ridley
Scott. Sigourney and producers talked to Ridley Scott briefly about
making another
Alien, but he couldn't get it together because he had just completed
Someone To Watch Over Me (1987) and was preparing Black Rain (1989) and was scheduled
to shoot Thelma And Louise (1991).

Source Quote

The producers' ideas ranged from the aliens invading Earth, where
they fuse into a giant, multi-talented monster that destroys New York
City to Ripley and Newt hunting an especially mobile creature in a Blade
Runner-esque off-world Metropolis, and then unsatisfied with these
concepts, Hill, Giler and Carroll eventually returned to what worked in
the first two films, a dark, isolated, labyrinthine setting. And they
soon found themselves returning for input, both because they had respect
for her judgment and because they thought she'd be more likely to
reprise her role if they brought her in as co-producer to help the story
and Lieutenant Ripley evolve. (Cinescape, 1992)

Hill and Giler each labored
on several ideas before settling upon a complex two part story that
offered the underhanded Weyland-Yutani Corporation (known as "The
Company") facing off with militarily aggressive culture of humans whose
rigid socialist ideology has caused them to seperate from Earth Society.
Weaver would only make a cameo appearance in it demanded that Alien 3
and Alien 4 be produced concurrently to lessen production costs. "We talked to Ridley briefly" said Weaver, who was enthusiastic about the possibility of working with Scott again. "But he could never get it together."
The director had just completed Someone To Watch Over Me and was
preparing Black Rain. He was also scheduled to shoot Thelma and Louise,
the feminist road picture for which he would receive and Academy Award
nomination. Though interested in returning to the franchise, he was
woefully overcommitted. (Sigourney Weaver, Cinescape 1992)